Technically speaking, this double role creates a number of difficulties for the actor. He has to perform with a partner who is not there. He has to interact with someone who is only wind, but the ghost’s response determines a vast range of things. This answer, which will be shot immediately after or the next day, and again the person to whom it is addressed is absent. Audiences and even people in the trade can hardly imagine the degree of concentration, the continuous replacement of I with you, that was needed to create the effect obtained by the director. Happy is the actor whose performance rests on an idea. This time round that was the case for me. I discovered once again that film is the ultimate art for expressing my feelings.
Conrad Veidt, “B.Z. Mittag”, March 19, 1926

The film tries to analyze characters using just one actor to represent fundamentally different human beings. We cannot deny that Conrad Veidt did not manage to make these two characters convincing. The camera did not always succeed in making us believe that they were two different individuals. In the scene where the two brothers confront each other, it often seems that they do not look at each other, that they move around one another without seeing each other, which weakens the overall effect. (…) We are less than satisfied because we read the novel. And Kellermann did not conceal his hope that they would make a serious film out of it that would stress his ideas and thus become a social and economic warning. If Kellermann saw the film, it is hardly likely that he would think it corresponds with viewpoint of the novel. The details that remain are insignificant to the author, merely external aspects; in other words, everything that was cinema in the old meaning of the word. It is all the more a shame because for once a social film could have shown active men belonging to different social strata.
Anonymous, Die Brüder Schellenberg, “Filmschau”, March 1926

“He speaks little and slowly, taking long pauses to think. He thinks slowly and consciously. He takes time because he knows what his objectives are. In the midst of a noisy, boisterous, irritating chaos, at its busiest centre, Potsdamer Platz, there is another world. It is almost a miracle to find an office in which silence and calm stability reigns. It is Grune’s office at Ufa. Today he has seen five hundred faces. He chooses every walk-on role himself. He’s dead tired. Yet he is ready to spend two hours talking about a short scene in the script which has to be changed and once again his words are so clear, placid, sure and calm, as if he were sitting in the shade of old oak trees on his land in the country. He is self-assured and, after five minutes, anyone has faith in him, in his goodwill and in his artistic capacity. They would have faith in him, even ignoring the fact that they are sitting in front of the director of Die Straße and Schlagende Wetter.

Very rarely have I seen a man with a vision which is so mimetic. There are indeed few directors who are capable of rejecting a scene twenty times in a script submitted by their own screen writer until he ‘gets it right’ – and he does. Very seldom does the writer believe the rejection to be justified. (…) Thousands of words wasted… Grune doesn’t speak more than ten words. And if the writer has learned something, then a miracle happens. The most terrifying work for a script writer, the destruction and rebuilding of an edifice which was already there, in this case delights him because even destruction becomes a productive process when you are working side by side with such a fertile mind as this.

Like all consistent men, he sometimes seems inconsistent. He never may be pushed but quite often he may be convinced. A scene is suggested to him. He still doesn’t see it. He rejects it. Yet during the day the author visualises it more clearly. The following morning he is able to re-enact it – obviously clumsily, in amateur fashion, but he manages it. Grune pauses for five, ten minutes, then corrects here and there certain nuances which might ring falsely, and accepts the rest. I have the feeling that, generally speaking, only with Grune have I learned to mould a scene in a way which is real, to the point where my visual and mimetic capacities are fully realised”.

(Willy Haas, Zusammenarbeit mit Grune, Film-Kurier, no.218, 16/9/1925; now in Willy Haas. Der Kritiker als Mitproduzent, by W. Jacobsen, K.Prümm and B.Wenz, Berlin, Hentrich, 1991)